The present invention relates generally to insulation concepts and in particular to insulation arrangements for machinery such as air compressors.
Many commercial and industrial air compressor devices are utilized in work areas where the maximum noise level allowable is regulated by the government or is controlled based upon the general desire of those controlling the work area to provide a comfortable working environment. One work environment where substantial levels of noise can and are generated involve work areas where machinery such as air compressors are present. Although a variety of mechanical devices of different designs are utilized to provide compressed air for the workplace, there are several common features used in the design of most industrial air compressors. Included in these common features are an outer enclosure of steel or other rigid material, the necessary mechanical and electrical components to produce compressed air, and acoustical insulation materials placed so that they are between the enclosure and the noise-generating mechanism that produces the compressed air.
In many cases the environment in which the air compressor device is used exposes the enclosure, insulation and mechanical components to extremes in temperature, saturation by water, dirt, dust, and chemicals as well as exposure to various airborne particulates, liquids and vapors. The compressor must be designed so that the mechanical and electrical components and the acoustical insulation will perform as designed under any of these extreme conditions.
Much time and effort has been put into the design of electric motors, mechanical pumps and other machinery components over the years in an attempt to insure that these devices will not only function under extreme environmental conditions, but will at the same time hopefully meet or exceed various governmental and environmental rules and regulations. On an ever-increasing basis, there have been concerns and additional governmental regulations addressing the varous noise levels in the work place and in view of these concerns and additional regulations, attention has been focused on the development of effective sound-insulating materials and designs which will not only meet the required regulations as to noise abatement, but will also perform under the environmental extremes.
Unfortunately, to date, efforts seem to have been focused on one or the other of these two objectives, but not on both. Certain efforts have been directed to very high-quality sound-absorbing or sound-deadening designs, but these have not been designed in a manner so as to meet or exceed all the constraints imposed by the environmental extremes. Acoustical insulation designs which have a greater likelihood of success under the extreme environmental conditions described above, have not proven to be as effective in the area of sound reduction.
To date, the more common insulating materials have been either a flexible urethane foam or a fiberglass insulation material. Usually a facing is put on the exposed surface of both materials in an attempt to make them more durable for use in the environment with its various extremes. However, both of these materials have critical drawbacks when used in this particular application.
Urethane foam can be produced so that its cell structure is comprised of a large percentage of "closed cells" that will not absorb moisture, oil or other liquids. However, there will be some percentage of open cells in this urethane foam structure that can absorb moisture, oil, or other liquids. Once this material begins any type of absorption of moisture, oil or other liquids, this will reduce the acoustical insulation qualities of the urethane foam. Urethane foam is also a fairly delicate material which is susceptible to tearing and other damage due to handling and assembly into machinery. While some of this susceptibility to damage can be reduced by covering the urethane foam with a suitable facing material, the urethane foam is substantially more expensive than is fiberglass, approximately three times more expensive for the same thickness and density. If a facing material must be added to this more expensive urethane foam as a protective covering, this results in making the overall package even more expensive. Further, urethane foam does not perform as well as fiberglass in noise-absorption tests when using the same thickness and density of material.
With regard to fiberglass insulation, it is a much better sound-absorbing material than is urethane foam in its manufactured form. Fiberglass insulation is also more cost-effective in that it costs approximately one-third of urethane foam. However, there are certain drawbacks to the use of fiberglass insulation material and these drawbacks include the open fibrous nature of the material. This openness makes fiberglass insulation more prone to moisture absorption. If a liquid saturates the material, its sound-absorbing or sound-deadening qualities are dramatically reduced. Consequently, if the air compressor in which this fiberglass insulation may be used comes in contact with water or oil or other liquids, the open fibrous nature of the material allows absorption and an effective elimination of any sound absorbing or sound deadening properties.
With regard to air compressor designs, those which are of the enclosed type typically rely on some type of air flow in order to cool the electric motor or piston engine which is located inside. The piston engine can also generate an extreme air flow condition for exhausting its engine exhaust from the enclosure. These air flow extremes when blowing up against the open fibrous fiberglass insulation can actually erode fibers from the batting and this also has a negative effect on the sound absorption performance of the fiberglass insulation. This situation makes some form of a covering a necessity with fiberglass insulation. However, facing on one or both sides of the fiberglass insulation alone will not eliminate all the negative conditions because cut-outs must still be made through the material in order to allow pipes, wires and other functional conduits to extend through the insulation.
While the present invention focuses primarily on the specific design concept of acoustical insulation for air compressors and similar machinery, there are certain designs and insulation concepts which are disclosed in prior patents which may be of interest with regard to a more complete understanding of the background of the present invention.
Mueller (Pat. No. 4,359,085 issued Nov. 16, 1982) discloses in its exemplary embodiment two machines which are arranged in a common cabinet-like housing which is insulated toward the interior from sound conducted through solids and airborne sound. In order for fresh air to be supplied to the machines within the housing, common fresh air channels are provided which are connected by way of an inlet port to the exterior air. In order to discharge the exhaust air, there is a separately arranged exhaust air series of chambers and/or exhaust air channels which discharge into the open air by way of an common outlet port. The sound-attenuating material which is used in this design consists of two Unshaped covering parts 14 and 15 which are lined with a sound-attenuating material which is intended to insulate the housing toward the exterior from sound conducted through solids and any airborne sound. This is believed to be a fairly typical approach followed and there are not really any specifics given as to the interior design details of these two Unshaped members.
Holdsworth (Pat. No. 4,347,042 issued Aug. 31, 1982) discloses a motor compressor unit and a method of reducing noise transmitted therefrom. The motor compressor unit comprises a compressor for compressing a vapor, a motor for driving the compressor, a shell encompassing the compressor motor, and a supply of lubricant disposed within the shell. The motor compressor unit further comprises a lubricant-absorbent fibrous material which is positioned against the interior surfaces of the shell for dampening sound waves which are generated within the motor compressor unit. The sound dampening materials referred to include lining 20 and cover 22 and as indicated, the lining is intended to be of a lubricant-absorbent fibrous material which would of course reduce its sound-dampening abilities over that of dry material due to the enhanced sound transmission results through liquid as opposed to through air.
Crago (Pat. No. 4,264,282 issued Apr. 28, 1981) discloses an air compressor apparatus which includes noise-reducing means arranged in the form of a noise-reducing enclosure. The air compressor is disposed within a cabinet wherein the inlet and outlet channels that conduct air into and out of the enclosure are lined with sound-absorbing material. This material is an acoustical foam and is provided on these inlet and outlet chambers in order to absorb sound waves originating with the air compressor and passing through these chambers.
Davis (Pat. No. 4,150,913 issued Apr. 24, 1979) discloses a blower for industrial vacuum machinery which is constructed using an impeller with backward curved plates for flow stability and high efficiency under varying conditions. A muffler for the discharge of the blower is provided and noise-deadening material 66 is used to line compartments 58 and 59 and the material selected is a polyurethane packing material of the type used for protection of parcels against breakage. In particular, this material includes a plurality of bubbles which are incorporated in the foam. Again, this particular design like that of Crago is believed to focus on fairly basic approaches where the sound-absorbing or acoustical insulation material is simply exposed foam or fiberglass of similar open material which would suffer from the moisture-absorption concerns and air velocity concerns previously mentioned. These particular prior devices although showing the use of insulation material in the design of air compressors and similar machinery do not focus to any degree on the specific construction, nor do these designs address the problems alluded to above. Other patents are believe to fit into this same general category as the foregoing devices of Mueller, Holdsworth, Crago and Davis. For example, Brink et al. (Pat. No. 4,022,550 issued May 10, 1977) and Van-Hee et al. (Patent No. 3,989,415 issued Nov. 2, 1976) are directed to the same types of concepts and sound-absorption or sound-deadening approaches as the first four patents mentioned.
There are further series of patent references which may be appropriately grouped as to one general type and these include panel designs where the noise-making component is insulated by some type of enclosing or surrounding insulation material disposed between that particular component and an outside enclosure or shell. Representative of this grouping of patents are the following:
______________________________________ Pat. No. Patentee Issue Date ______________________________________ 4,411,592 Traver et al. 10/25/1983 3,947,148 Holt 03/30/1976 3,778,184 Wood 12/11/1973 3,736,074 Kilbane et al. 05/29/1973 3,688,867 Antonetti et al. 09/05/1972 3,676,012 Brockie 07/11/1972 3,462,949 Anderson et al. 08/26/1969 3,360,193 Harris et al. 12/26/1967 2,296,702 Butler et al. 09/22/1942 1,773,909 Korb 08/26/1930 ______________________________________
In each of the foregoing listed patents, very little attention is given to the specific construction and material selection of the sound-absorbing insulation material. While some attention is given to different insulation concepts in the Antonetti patent, as referenced in FIGS. 4 and 5, the concerns addressed by the present invention are not the focus of any of these earlier inventions. For example, in Korb (Pat. No. 1,773,909), reference to the insulating material indicates that it is only a "suitable" insulating material such as asbestos. In any environment where moisture or liquid absorption was a risk, this material would not be suitable used in this manner in view of its ability to absorb moisture and as a result the loss of any acoustical insulating properties.
Hornady (Pat. No. 2,235,962 issued Mar. 25, 1941) discloses an insulation panel which is used in combination with a refrigerating apparatus. The particular baffle shown includes a frame member 54 which supports a pair of screen elements 56 which in turn hold asbestos fibers 57 in place. The patent indicates that the asbestos fibers very effectively silence the noises yet do not deteriorate when exposed to the flow of lubricant and refrigerant. This patent also points out that sponge rubber which may have been used previously in order to deaden compressor noises could not be used in the cylinder head. What is not addressed in this particular patent as might be expected from its date of issue are the problems with the use of asbestos. As the industry has gone away from the use of asbestos, it has run head-first into the problems of using such materials as sponge rubber and open-cell foam or fiberglass, the same problems which the present invention addresses.
Guess et al. (Pat. No. 3,821,999 issued Jul. 2, 1974) discloses an acoustical liner consisting of a perforated honeycomb sandwich panel wherein the axes of the honeycomb cells are tilted relative to the outer surface for more effective absorption of high amplitude sound and shock waves over a relatively narrow band of the frequency spectrum. While this particular patent focues more specifically on the design of an acoustic liner and an application to specific sound frequencies, it does not address the concerns of the present invention with regard to air compressor noises and the use of an acoustical insulation design in an environment where exposure to moisture and other liquids is possible.
The present invention provides an acoustical insulation system that eliminates the previously outlined drawbacks of using standard fiberglass or urethane foam materials. The present invention Contemplates an improvement to the specific prior designs discussed above in that it provides the superior acoustical properties of fiberglass (as compared to flexible urethane foam) and it solves the problem of moisture/liquid absorption. The present invention is cost-effective in that it is significantly lower in cost than commonly used flexibe urethane foam materials and it holds up and performs under a wide variety of temperature and other environmental conditions including extreme air velocities flowing through the air compressor.